A dense wave of smog began Process_start in Northeast China , especially in major cities including Harbin , Changchun and Shenyang , as well as the surrounding Heilongjiang , Jilin , and Liaoning provinces on 20 October 2013 .

In Changchun , air pollution recorded Recording at an all-time high and the levels of PM particulate matter rose Cause_change_of_position_on_a_scale to 845 micrograms per cubic metre on 22 October 2013 .